Process for the separation of higher acetylene hydrocarbons



Oct. 23, 1962 A. woLFRAM ETAL PROCESS FOR THE SEPARATION OF HIGHER ACETYLENE HYDROCARBONS Filed 0G11. 6, 1959 mZON fmZON @z mmDmOm QZOUmm INVENToRs Arthur Wolfram PROCESS FR THE SEPARATEN F IMGHER ACETYLENE HYDROCUNS Arthur Wolfram and Harald Lorenz, Frankfurt am Main,

Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Brning, Frankfurt am Main, Germany, a corporation of Germany Filed Oct. 6, 1959, Ser. No. 844,732 Claims priority, application Germany Feb. 24, 1956 8 Claims. (Cl. 260-679) The present invention relates to a process for the separation of higher acetylene hydrocarbons. This application is a continuation-in-part of application Serial No. 641,160, tiled February 19, 1957, now abandoned.

Acetylene is frequently used in industry as starting material for chemical syntheses, for example in the manufacture of vinyl compounds. It is known that the higher molecular weight acetylenes act as contact poison in these reactions. It is, therefore, useful to purify acetylene to a large extent by removing these higher acetylene hydrocarbons.

In the production of acetylene by pyrolysis of hydrocarbons, higher molecular weight acetylene hydrocarbons, such as methyl acetylene, diacetylene and vinyl acetylene are generally formed. It is ditlicult, but necessary, to separate these compounds, although they appear only in small amounts in the gaseous reaction product. It has already been proposed to separate these compounds to a large extent by fractional condensation. This procedure is dangerous, however, because it involves accumulation of diacetylene, which is known to have a pronounced tendency to explode. Acetylene produced by pyrolysis and subjected to fractional condensation generally contains about 0.05% by volume of diacetylene in addition to the other homologues thereof, thus indicating that the aforesaid higher acetylene hydrocarbons are only incompletely separated.

It has also been proposed to remove higher molecular weight acetylenes from the crude gas obtained by pyrolysis of gaseous hydrocarbons by washing the latter with solvents or hydrocarbon oils, the washing agent used being recycled. This process involves the disadvantage that the solvent used must constantly be regenerated. Regeneration is brought about by heating or blowing, but the diacetylene is only incompletely expelled and partially polymerizes to yield products that likewise tend to explosions.

-Itis also known (Patent 2,236,978) to scrub acetylenecontaining gas mixtures at room temperature and under a pressure of ll atmospheres (absolute) in only one stage with hydrocarbon oils in order to remove all compounds less volatile than acetylene therefrom and, if desired, to pyrolyze a part of the scrubbing liquid together with the compounds dissolved therein. However, the amount of hydrocarbon that is necessary for scrubbing to remove all of the higher molecular weight acetylenes is far greater than the amount that can be pyrolyzed in the pyrolysis apparatus. If the amount of washing liquid used were limited to the amount that can be pyrolysed, and the same pressure of 11 atmospheres (absolute) were used to attain complete separation of the higher molecular weight acetylenes, very low scrubbing temperatures, viz. -60 C. to y 65 C., would have to be employed, thereby rendering this process uneconomical.

If a larger amount of hydrocarbon washing liquid is used than can be pyrolyzed in the pyrolysis apparatus, the compounds less volatile than acetylene must be expelled from the portion that is not pyrolyzed. These compounds consist to a high extent of highly explosive substances, such as diacetylene, vinyl acetylene, acetylenes 3,0524? Patented 0ct. 23, 1952 having the formula CSHG, such as divinyl-acetylene, and additionally of less explosive substances such as allene, methyl acetylene, dimethyl-acetylene, ethyl-acetylene, and propylene. The removal of the compounds that are less volatile than acetylene from the scrubbing liquid, is eneumbered with great danger, i.e. in the possibility that explosions of the expelled gases and in particular of diacetylene may occur, and with the disadvantage that especially the most dangerous compound, viz. the diacetylene, cannot be completely expelled, but is partly polymerized to compounds which are likewise explosive.

Additionally the use of such large amounts of scrubbing liquid is accompanied by the disadvantage that large amounts of the desired acetylene are dissolved by the hydrocarbon oil and accordingly would be lost if the hydrocarbon oil were directly pyrolyzed.

This invention provides a two-Stage process for the removal of higher molecular weight acetylenes and other compounds that are less volatile than acetylene from acetylene-containing gases obtained in pyrolysis processes in which at least one liquetlable hydrocarbon containing at least 3 carbon atoms is pyrolyzed. According to the invention, the gases obtained by the pyrolysis are washed in the hrst stage at a temperature between 0 and 50 C. with at least one hydrocarbon which is liquid under the operating conditions and contains at least 3 carbon atoms, and in the second stage at a temperature above -50 C. with a hydrocarbon that is liquid under the operating conditions of this second stage. The wash solution from the lirst scrubbing stage is fed to the pyrolysis zone. The wash solution from the second scrubbing stage is subjected to degassing to remove the hydrocarbon gases absorbed in the second stage. These hydrocarbon gases are advantageously added t-o the crude gas entering the rst scrubbing stage and the degassed wash liquor is recycled to the second scrubbing zone. After a short time of operation, equilibrium conditions are established in which the C4 and C3 hydrocarbons are absorbed by the washing liquor in the irst scrubbing stage at substantially the same rate they are formed in the pyrolysis zone and all of said washing liquor, including the absorbed C4 and C3 hydrocarbons, is fed to the pyrolysis zone.

'Ihis elect is possible because the recycling of the expelled gas from the second stage to the crude gas increases the amount of the Cg-hydrocarbons (i.e. methylacetylene, propylene and allene) and, therefore, the partial pressure of said components. The partial pressure then becomes at least so high that the amount of C3- components absorbed in the first washing step equals that formed in the pyrolysis unit. The major part of the C3-components passes through the iirst stage and is absorbed in the second stage. Thus it is an important and preferred embodiment of our invention that the application of two washing stages and recycling of the gas expelled from the washing liquid of the second stage of the crude gas makes it possible to absorb in the first stage all of the C3- and C4-hydrocarbons newly produced in the pyrolysis unit without, however, requiring an amount of washing liquor that is too great to be fully utilized in the pyrolysis zone.

The present process may be applied to crude gas mixtures which have been formed by pyrolizing the abovementioned hydrocarbons or, if more convenient, gas mixtures, in which the acetylene is enriched or to a prepuriytied acetylene which has been obtained by partly working up said crude gas. The term at least liqueable as used herein means liquid hydrocarbons and normally gaseous hydrocarbons which are liquid under the operating conditions. At any rate, these hydrocarbons are used in the present process in the liquid state. lIn carrying out the present process it is immaterial whether pure hydrocarbons are pyrolyzed or a mixture of hydrocarbons, which latter is more advantageous from an industrial point of view.

In carrying out the process of this invention it is useful to operate at low temperatures of between, for example, about C. and 50 C., preferably between about 10 C. and 40 C. and, advantageously with application of pressure up to 35 atmospheres, e.g. between 5 and atmospheres, and preferably between 7 and 16 atmospheres, so as to utilize fully the dissolving power of the washing liquid and so as to be able to Wash out 4a maximum amount of gas with a minimum quantity of washing liquid. Higher pressures are advantageously applied at relatively high temperatures, and relatively low pressures preferably at relatively low temperatures. The partial pressure of the acetylene should not be above about 3 atmospheres, preferably not above about 1.5 atmospheres.

VThe process of this invention may be carried out by spraying the washing liquid over lling material or bubble plates so as to promote a good contact with the gas, preferably counter-current. Further variants of the process of this invention are obvious to those skilled in the art.

The process of this invention has the advantage of completely or almost completely removing the explosive ingredients of the crude gas or the acetylene in the first stage. It also removes a great part of the propylene and the C3H4, i.e. the considerably less harmful methyl acetylene and its harmless isomer, aliene. The residual amounts of the last-mentioned compounds are then separated in the course of the second washing stage in which the pressure and temperature applied are in the abovementioned ranges. Due to the relatively small danger involved in handling methyl acetylene, the solvent used in the second Washing stage may be recycled without any considerable risk. To this end, the dissolved methyl acetylene, allene, propylene, and the dissolved hydrocarbon portions of the crude gas freed from higher acetylenes are again removed from the solvent, for example by heating and/or evacuating and/or blowing out. Though these hydrocarbons are preferably added to the crude gas entering the first scrubbing zone, they may also be recovered in a pure form, or be pyrolized.

In carrying out the process of this invention using lowboiling hydrocarbons as washing liquid in the second stage, it is advisable that the Washing liquid entrained with the acetylene gas be removed by washing with a high-boiling hydrocarbon, preferably with the hydrocarbon to be fed to the pyrolysis zone, or a high-boiling fraction, under normal or raised pressure, at room temperature or at lower temperature, including the pressure and temperature ranges indicated above. These high-boiling hydrocarbons are advisably introduced, as is the washing liquid, into the pyrolysis apparatus. It is evident that they may be pyrolized alone and together with fresh oil.

As washing liquids there may be used in the first washing stage hydrocarbons or hydrocarbon mixtures used in the pyrolysis or single fractions thereof which are liquid or liqueable under the reaction conditions, such as propane, nor iso-butano or iso-butylene, pentane, hexane, octane, isooctane, diisobutylene, decane, dodecane, preferably in the form of the usual technical mixtures, for example those which contain cycloaliphatic portions, such as cyclohexane, or topped oil. There may be used narrow or broad fractions of hydrocarbons, for example those rich in pentanes, hexanes, octanes or decanes. The aforesaid hydrocarbons, may also constitute or contain unsaturated compounds. Since aromatic hydrocarbons, for example benzene, toluene or Xylene, which may be formed in the pyrolysis process, are also absorbed in the first washing stage and together with the washing agent are recycled into the pyrolysis unit, in the pyrolysis section, the formation of new portions of such aromatic hydrocarbons is prevented.

As washing liquid in the second washing stage there may be used all solvents which are liquid or liqueiable under the reaction conditions and capable of sparingly dissolving acetylene and readily dissolving methyl acetylene, C3H5 and allene. There may chiey be employed hydrocarbons, for example fractions thereof with a narrow boiling range, or the products mentioned to be suitable washing agents in the rst stage. These hydrocarbons may, if desired, also be introduced into the pyrolysis apparatus, for examply after having repeatedly been recycled, or a small portion thereof may continuously be introduced into the pyrolysis apparatus; a further variation consists in conducting the solvent of the second scrubbing stage-after at least partially degassing it-into the rst scrubbing stage and then into the pyrolysis apparatus. If it is not intended to pyrolize the washing agent of the second scrubbing stage, aromatic hydrocarbons such as benzene, toluene, and the xylenes may also be used as washing agent in the second stage.

The process of the invention is diagrammatically illustrated in the accompanying drawing.

The following example, in which reference is made to the drawing, sets forth the best mode now contemplated by the inventors of carrying out the invention, but it is not intended to limit the scope of the invention thereto:

EXAMPLE Light gasoline is pyrolized in a pyrolysis zone to obtain 10,000 Nm3/hour of a crude gas consisting of 13.1% by volume of acetylene 7.8% by volume of ethylene 1.5% by volume of propylene 0.4% by volume of C3H4 0.4% by volume of C4H2 1.3 by volume of C4H4 10.2% by volume of methane, and

65.3% by volume of gas mixture (hydrogen, carbonmonoxide, carbon dioxide and nitrogen),

which is conveyed from gasometer 2 to compressor 3 and then concentrated to a pressure of 10 atmospheres absolute. The concentrated gas is then conveyed to a iirst washing column 4 Where the C4-acetylenes are washed out with light gasoline entering by way of line 5. For working up the 10,000 Nm.3/hour of crude gas, about 5 tons/ hour of light gasoline of a temperature of 20 C. are necessary for removing 99.9% of the C4-acetylenes. The gasoline from washing column `4 containing the absorbed C-acetylenes is fed to pyrolysis zone 1 by way of line 6. The residual portion of the less soluble Ca-hydrocarbons, i.e. the compounds C3H4 and Cgi-I6, is removed from the gases leaving washing column 4 by Way of line 7 at about the same temperature in a second Washing column 8, using a light gasoline boiling at about C. (C7- fraction) as washing liquid which is introduced at 9, but may be introduced at any place into the solvent cycle between columns 8 and 10. The operation temperature of 20 C. implies the use of about 23 tons/hour of light gasoline in order completely to remove 99.9% of the C3- hydrocarbons. The washing liquid charged with the C3- hydrocarbons is then released in valve V to a pressure of 1.4 atmospheres absolute and conveyed to degassing column 10, in which the liquid is heated by means of evaporator 11 to a temperature of, for example 60-70" C. and the C3-hydrocarbons are expelled.

The regenerated washing liquid is pumped by pump P through conduit 12 via heat exchanger 14 into washing column `8. The gas mixture consisting of C3-hydrocarbons and, partially, of Cg-hydrocarbons escapes from degassing column 10 and is reintroduced into gasometer 2 by way of -line 13, or added to the crude gas at any place before the first scrubbing stage, whereby the partial pressure of .the Cs-hydrocarbons in the crude gas 1s increased until an equilibrium is brought about in which the rate at which the Ca-hydrocarbons are washed out by the light gasoline in ythe first washing column 4 1s equal to the rate at which C3-hydrocarbons are produced in the pyrolyss zone 1. To render the process more economical, some cooling devices are necessary (not shown in the drawing). Purified acetylene free from undesirable C3 and C4 constituents leaves the system by way of line 15.

The following Table I is a material balance of the method specifically described by way of example. Column A shows .the composition of the crude gas obtained by pyrolysis, B of the gas dissolved in rst washing column 4, C of the gas dissolved in second washing column 8, and R is the sum total of CO, CO2 and N2, D shows -the composition of the crude gas, which is obtained by admixing the gases liberated `from the second-stage scrubbing liquid (listed in column C) with .the crude gas of column A. Thus column D is obtainable by simple addition of the gas listed in columns A and C and indicates the composition of the gas entering the iirst scrubbing zone 4. Column E indicates the composition of the scrubbed gas, after it has left scrubbing column 8 by way of line 15. The data of column E are obtained by subtracting `the values of column B -from those of column A and indicate how closely the rate of absorp- :tion of the C4 and C3-hydrocarbons in the lirst scrubbing zone match the rate of production in the pyrolysis zone.

Table I If the gases dissolved in washing column 8 are not recycled and admixed with the crude gas, the Afollowing values, listed in Table II, are obtained:

Table Il We claim:

1. A process Afor removing C3, C4 and higher acetylenes from a crude acetylene-containing `gas which comprises washing said gas in a rst scrubbing zone at a temperature between about 0 C. land 50 C. with a hydrocarbon that is liquid at said temperature for dissolving all of the C4 and higher acetylenes and a portion of the C3 acetylenes in said hydrocarbon, pyrolizing all of said hydrocarbon used together with the dissolved C4 and higher acetylenes and a portion of C3 acetylenes, washing the Agas from said irst scrubbing zone in a second scrubbing zone at a temperature above about 50 C. with a hydrocarbon that is liquid at said temperature for dissolving the residual C3 acetylenes in said hydrocarbon, degassing the hydrocarbon from said second scrubbing zone to recover said residual C3 acetylenes, and recycling recovered C3 acetylenes to the crude gas entering said rst scrubbing zone.

2. A process -for removing C3, C4 and higher acetylenes from a crude acetylene-containing gas which comprises washing said gas in a rst scrubbing zone at a temperature between about 0 C. and 50 C. with a hydrocarbon that is liquid at said temperature for dissolving all of the C4 and higher acetylenes and a portion of the C3 acetylenes -in said hydrocarbon, pyrolizing all of said hydrocarbon used together with the dissolved C4 and higher acetylenes and a portion of C3 acetylenes, washing the gas from said rst scrubbing zone in a second scrubbing zone at a temperature above about 50 C. with a hydrocarbon -that is liquid at said temperature Ifor dissolving the residual C3 acetylene in said hydrocarbon, degassing the lhydrocarbon 'from said second scrubbing zone to recover said residual C3-acetylenes, recycling recovered C3 acetylenes to the crude gas entering said rst scrubbing zone, and recycling the liquid hydrocarbon liberated yfrom said residual C43-acetylenes into the second scrubbing zone.

3. Process as defined in claim 1 wherein cthe washing in the first scrubbing zone is conducted at a pressure of between 5 and 20 atmospheres.

4. Process as defined in claim 1 wherein the partial pressure of acetylene is maintained below about 3 atmospheres in the first scrubbing zone.

5. Process as defined in claim 1 wherein the irst and second scrubbing zones are maintained at temperatures between about 0 C. and 50 C. and at pressures between 5 and 20 atmospheres, and the partial pressure therein of acetylene is below about 1.5 atmospheres.

6. Process as defined in claim 1 wherein the rst and second scrubbing zones are maintained at temperatures between about 10 C. and 40 C. and at pressures between 7 land 16 atmospheres, and the partial pressures therein of acetylene are below about 1.5 atmospheres.

7. A process for removing C3, C4 and higher acetylenes from a crude acetylene-containing gas which comprises washing said gas -in a rst scrubbing zone at a temperature between about 0 C. and 50 C. with a hydrocarbon that is liquid at said temperature -for dissolving all of the C4 and higher acetylenes and a portion of the C3- `acetylenes in said hydrocarbon, pyrolizing all of said hydrocarbon used together with the dissolved C4- and higher acetylenes and a portion of C3-acetylenes, washing the gas yfrom said rst scrubbing zone in a second scrubbing zone at a temperature above about 50 C. with a hydrocarbon that is liquid at said temperature for dissolving the residual C3-acetylenes in said hydrocarbon, degassing the lhydrocarbon from said second scrubbing zone containing said residual C3-acetylenes in a degassing zone and admixing the gas mixture comprising C3-acetylenes with the crude acetylene-containing gas, the portion of C3-acetylenes dissolved in the hydrocarbon in said first scrubbing zone being about equal to the amount of C3-acetylenes produced in the pyrolysis step.

8. A process Afor removing C3-, C4- and higher acetylenes from a crude acetylene-containing gas mixture which comprises washing said gas mixture in a first scrubbing zone, at a temperature between about 0 C. and 50 C. and in the presence of C3-acetylenes added to said mixture in excess of the original C3-acetylene content of the mixture, with a hydrocarbon that is liquid at said temperature for dissolving all of the C4- and higher acetylenes and substantially all of the original C13-acetylene content of said mixture, pyrolyzing all of said hydrocarbon used together with the dissolved C4- `and higher acetylenes Iand a pon-tion of the C3-acetylenes, washing the 'gas from said 'irst scrubbing zone in a sec` ond scrubbing zone at a temperature above about 50 C. with a hydrocarbon that is liquid at said temperature for dissolving .the residual C3-acetylenes in said hydrocarbon, degassing the hydrocarbon from said second scrubbing zone containing said residual C3-acetylenes in a degassing zone, and admixing the gas comprising C3 acetylenes with the crude acetylene-containing gas mixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,180,496 Bolc-ar Nov. 21, 1939 2,236,978 Taylor Apr. 1, 1941 2,830,677 Coberly Apr. 15, 1958 2,834,431 Fauser May 13, 1958 

1. A PROCESS FOR REMOVING C3, C4 AND HIGHER ACETYLENES FROM A CRUDE ACETYLENE-CONTAINING GAS WHICH COMPRISES WASHING SAID GAS IN A FIRST SCRUBBING ZONE AT A TEMPERATURE BETWEEN ABOUT 0*C. AND -50*C. WITHIN A HYDROCARBON THAT IS LIQUID AT SAID TEMPERATURE FOR DISSOLVING ALL OF THE C4 AND HIGHER ACETYLENES AND A PORTION OF THE C3 ACETYLENES IN SAID HYDROCARBON, PYROLIZING ALL OF SAID HYDROCARBON USED TOGETHER WITH THE DISSOLVED C4 AND HIGHER ACETYLENES AND A PORTION OF C3 ACETYLENES, WASHING THE GAS FROM SAID FIRST SCRUBBING ZONE IN A SECOND SCRUBBING ZONE AT A TEMPERATURE ABOVE ABOUT -50*C. WITH A HYDROCARBON THAT IS LIQUID AT SAID TEMPERATURE FOR DISSOLVING THE RESIDUAL C3 ACETYLENES IN SAID HYDROCARBON, DEGASSING THE HYDROCARBON FROM SAID SECOND SCRUBBING ZONE TO RECOVER SAID RESIDUAL C3 ACETYLENES, AND RECYCLING RECOVERED C3 ACETYLENES TO THE CRUDE GAS ENTERING SAID FIRST SCRUBBING ZONE. 